Coded track circuit signaling system



July 18,- 1944- w. H. RElcHARD CODED TRACK CIRCUIT SIGNALINCT SYSTEM Filed July 17, 1942 5 Sheets-Sheet l FIG.. LA.

2 H (Stays down) 1H-(Holden }A 4 I lNVENToR by ATTORNE'Y July 18, 1944. w. H. REICHARD CODED TRACK CIRCUIT SIGNALING SYSTEM Filed July 1'7, 1942 3 Sheets-Sheet 2 v ATroRN'EY yJuly 18, 1944.

W.l H. REICHARD CODED TRACK CIRCUIT SIGNALING SYSTEM I Filed Julyiw, 1942 3 Sheets-Sheet 3 INVENTo ZU .A4

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BY m A ,VATTORIY Patented July 18, 1944 Conni) TRACK CIRCUIT SIGNALING SYSTEM Wade H. Reichard, Rochester, N. Y., assigner to General Railway Signal Company, Rochester,

Application July 17, 1942, Serial No. 451,272

Claims.

The invention relates to signaling systems for railroads using coded track circuits, and more particularly to an organization for preventing a false signal indication in the event of the failure of the insulated joints separating adjoining coded track circuits, even though the polarity of the energization of the track rails of one track section is suitable for operating the code following track relay for the adjoining track section.

I In the conventional coded track circuits commonly used in railway signaling for the control of automatic block signals or the like, a breakdown of the insulated joints in the track rails electrically separating adjoining track sections, or a low resistance leakage path around such joints, tends to permit the energization of the track relay of one track section by the energizing potential applied to the track rails of the adjoining track section, with the result that a false clear signal or like control may be given. In order to protect against this contingency, it has been proposed to employ a polarized track relay and apply an energizing potential to the track rails of the adjoining track section of a polarity' which will not energize the track relay. If a stray potential of a polarity suitable for operating the track relay should exist, however,l a false intermittent operation of the track relay may occur with broken-down joints under favorable conditions due to the intermittent neutralization of the stray potential by the coded potential applied to the other track section. Also, in the various applications of coded track circuits, it is sometimes desirable to use an energizing potential for a track section which is of a different polarity under different conditions, either as a direct or driven code pulse or as an inverse or off code pulse; and under such conditions, the protection against broken-down joints afforded by the expedient of using staggered polarities is lost.

In view of these and other considerations, it is proposed in accordance with the present invention to provide an organization of code transmitting and code responsive means for adjoining track sections in a coded track circuit system which will afford the desired protection against failure of the insulated joints separating these track sections, and without relying upon the expedient of staggered polarities.

Generally speaking, and without attempting to dene the nature and scope of the invention, it is proposed to employ a decoding means responsive to the intermittent operation of a code following track relay which requiresthis track relay to be successively energized with intervening deenergized periods, each of which are of limited duration, in order to establish a signal indication or other control less restrictive than stop, and to provide means eifective after this decoding means has been once deenergized by a passing train or the like to control the code pulses supplied to the adjoining track section in the rear so that in case of an insulated joint break-down the period of deenergization between the successive energizations of such track in the rear are of longer duration than said usual deenergized periods of limited duration. Thus, in the event of failure in the insulated joints separating two track sections, the track relay for the forward track section cannot be operated by the energization of the rails of the rear section in that particular manner required by said decoding means to give a signal indication or control less restrictive than stop.

y In other words, considering the invention as applied to a conventional automatic block signal system using coded track circuits, when the signal at the entrance to a given block has been put to stop by a train, the energization of the track relay for that section by the caution code pulses applied to the adjoining rear section, in the event of failure of the insulated joints, automatically mutilates these caution code pulses in a manner to prevent successive energizations of the track relay within the limited period of time requiredto energize the signalcontrol relay for clearing the signal, thereby preventing the signal from being falsely cleared under broken-down joint conditions in the absence of legitimate code pulses applied to its own block section.

. In the specic embodiment of the invention illustrated and described, these functions and mode of operation are obtained by employing slow release front and back Contact repeaters of the code following track relay, and controlling the energization of the signal control relay through a front contact of the back contact repeater and the supply of code to the block section in the rear through a back contact of said back contact repeater, so that there is a positive interlock, so to speak, which prevents an energization of the rails of the rear block section and an energization of the code following track relay for the forward section in the event of brokendown insulated joints at the time intervals required to energize the signal control relay.

The mutilation or chopping of the code delivered to a rear block section in the case of brokendown insulated joints causes in turn erratic and spasmodic operation of the code following track relay for the rear block section, tending to cause deenergization of its signal control relay, and in turn a mutilation or chopping of the code delivered to the next block section in the rear. In order to avoid the cascading or tumble-down effect tending to put to stop a series` of signals, provision is made to permit a signal control relay, once it has become energized, to be maintained energized by successive energizations of its code following track relay separated by longer periods of deenergization than `is required to initially energize the signal control relay, so that while a signal control relay will not pickup in response to the chopped code automatically produced, it will hold up in response to such chopped code.

The characteristic features, attributes and mode of operation of the organization of the present invention, in both its broad and specific aspects, will be in part apparent and in part pointed out in the following description of one specific embodiment of the invention.

The accompanying drawings illustrate in a simplified and diagrammatic manner one form of the invention applied to a typical automatic block signaling system, the parts and circuits being illustrated to facilitate an explanation and understanding of the nature of the invention, rather than to show the specific details of construction and arrangement of parts and circuits that would be employed in practice.

ln these drawings, Figs. 1A and 1B show one specic embodiment of the invention applied to the control of typical automatic block signals for three blocks; Figs. 2A, 2B, 2C and 2D comprise a series of explanatory diagrams indicating the character of the code pulses and the resultant signal indications for different conditions of train movement under broken-down joint conditions; and Fig. 3 is an explanatory diagram showing the sequence and relative times of relay operations for adjoining blocks under certain conditions.

In connection with the embodiment of the invention illustrated, it is assumed that the railroad track is divided into blocks by insulated joints in the usual way, with one coded track circuit for each block, and further that driven codes.

of a iixed polarity and without any inversel or oir codey pulses are employed for the control of the indications of the block signals only. The invention, however, is not limited to such an application, and may be applied to coded track circuits used for any purpose, and provided with code pulses of either a driven or an inverse code which are of different polarity at different times for approach lighting, highway crossing signal control, or other purposes, as well as for automatic block signal systems having cut sections to provide two or more coded track circuits for a block.

Figs. 1A and 1B, when placed end to end, illustrate the invention applied to three blocks or track sections TI, T2 and T3 of an automatic block signal system. The wayside signals I, 2 and 3 at the entrance ends of these track sections may be of any suitable type displaying any desired aspects. For simplicity, it is assumed that these signals are color light signals of conventional form giving stop, caution and proceed indications of red, yellow, and green, the stop indication corresponding to the absence of any code in the track rails of the corresponding block, the yellow or caution indication to a '75 code rate,

and the green or proceed indication to a code rate.

The equipment for each of the blocks or track circuits is the same, and referring to the track section T2 in Fig. 1B as typical, a code following track relay ZTR is connected across the track rails of this track section at the entrance end adjacent the signal 2 in the usual way. This track relay is preferably of the biased polarized type for sensitivity and quick response, but the use of a polarized relay is not essential, nor relied upon against false signal indications in the case of broken-down insulated joints. The track relay ZTR operates a contact nger 5 to energize a slow-release front contact repeater relay 2FP when the track relay is energized, and a back contact repeater relay 2BP when the track relay is deenergized, providing the repeater relay ZFP is then energized to close its front contact 6. The back contact repeater relay 2BP also energizes a repeater relay ZBPP. The energizing circuit for the home signal control relay 2H includes a front contact of the contact nger 5 of the track relay ZTR, and a front contact I of the back contact repeater 2BP, this front Contact 'I of the repeater relay 2BP being shunted by a front contact 8 of the relay 2H, in series with a front contact II of the repeater relay BPP, as can be readily seen in the drawings.

The coding operation of the track relay Z'I'R also operates a contact nger 9 to govern the energization of the primary of a decoding transformer II) and cause energization of a distant relay 2D in the we1l-known manner through a.

tuned circuit and full wave rectier, when the track relay is operating at the clear or 180 code rate.

At the other exit end of the track section T2 a track battery I2 is connected across the track rails in series with the usual limiting resistance I3, when a code transmitter relay 3CTP is energized; and provision may be made as shown to shunt the track rails when this transmitter relay 3CTP is deenergized. 3CTP is arranged to be connected to contacts of suitable code oscillators or motor driven code transmitters of the usual type operated at the different 75 and 180 code rates. When the home relay 3H for the next block in advance is energized, the transmitter relay 3CTP for the track section T2 is connected through the front contact I4 of the relay 3H to the contacts of the 180 code transmitter I80CT; but when the relay 3H is deenergized, the transmitter relay 3CTP is connected through back contact I4 of the relay 3H and a back contact I5 of the associated back contact repeater relay 3BP to the contacts of the 75 code transmitter 'I5CT, in a manner that will be readily apparent from the drawings.

Operation- While the insulated joints of the usual type and construction may lose their insu.

lating qualities, or a low resistance leakage path may develop around these joints at any time independently of train movement, it generally happens that a broken-down joint condition is created as a result of a train movement over the joints; and since it is the presence of a train which makes it unsafe to display a wrong signal indication, it is convenient to discuss the operation of the invention on the assumption that the insulated joints are broken down by a train movement.

As a typical example of the contemplated operation, and referring to the diagram of Fig. 2A,

assume that4 atrain travelling in the normal di- The transmitter relayv .rection of trafc indicated by the arrow moves into the-track section T3 beyond the signal 3 into the position shown. This causes the code following track relay STR. to remain dropped away which releases the relays SFP, SBP and 3H to close the circuit for the relay 3CTP through contacts I4 and I5 so that it is operated at the 75 code rate to apply a 75 code to the track section T2 from battery I2. that this train movement causes the insulated .joints at the signal 3 to break down and provide circuit pathsA as indicated by the dotted lines X to permit possible energization of the track relay STR of the track section T3 by the track battery `I2 for the track section T2 in the rear by reason of the '75 code being applied thereto. Under these conditions, however, the shunting action of the wheels and axles of this train not only prevents the false energization of the track relay STR from `.track section T2 and holds the signalS at stop, but also reduces the inter-rail potential provided by the track battery I2 for the track section T2 so that the track relay 2TR. is likewise maintained deenergized and the signal 2 at stop. Code pulses at the 75 code rate are thus applied to the second track section TI in the rear and cause the signal I to indicate caution in the usual manner. l When insulated joints break down under the conditions pointed out above, no unsafe signal indications are given, but there are added conditions which may occur in practice against which the present invention provides adequate protection to prevent unsafe signal indications.

In order to illustrate the utility and significance of the present invention, it is convenient to consider rst the operations of the'coded track circuit system that would occur under certain added broken-down joint conditions if the protective features characteristic of this invention were not employed. As the train in the track section T3 advances (see diagram of Fig'. 2B) it may reach a point where its wheel shunt is no longer effective to prevent energization of the track relay STR by the code pulses being Vsupplied to the track section in the rear. Also, it may happen that after the train leaves the track section T3 and removes the shunting effect upon the track relay STR, no code pulses aretransmittedover the track rails of this track section behind the train on account of some failure of the coding equipment, leaving the track relay STR free to follow without interference, the code pulses in the track section T2 in the rear on account of the broken-down insulated joints. Incidentally, it may also happen that a rail is broken by the train in its movement in track section T3, so that there is no shunting action on the track relay STR, and it is free to follow the coding in the rear track section T2. Under all of these various conditions, and without the -protective features of this invention, it can be seen that the coding operation of the track'relay STR (see Fig. 1B) Iby current improperly supplied to it around the broken-down insulated joints at signal 3, would first cause an energization of the signal control relay 3H, which in turn would increase the pulses in the track section T2 to the 180 rate and cause energization of the relay 3D, thereby causing signal 3 to display a false clear indication at the entrance to a block that may in fact be occupied, or at the entrance to a block when the next block is occupied. It is the object of this invention to prevent such improper signal indications under .these conditions.

Then let us further assume Let us .now consider how such false clear' indication is prevented by reason of this invention, and assuming that the track relay STR is free to be improperly energized by the code pulses applied to the .track section T2 in the rear on account of the failure of the insulated joints at signal 3, and because of the Various added conditions pointed out above where there may be-a loss of train shunt, no code following a train just entering the next succeeding track section T4 (not shown), or a broken rail in the. track section T3. When the contacts of the 75 code transmitter 15CT at signal 3 close and energize the transmitter relay SCTP through contacts I 4 and I5, the track relay STR is energized and in. turn its front contact repeater relay SFP is energized through front contact 5 aswill be readily apparent from Fig. 1B and as indicated diagrammatically in Fig. 3. Then, when the contacts of this 75 code transmitter 'I5CT are open, the relays 3CTP and SI'R drop, so as to energize the back contact repeater SBP through back contact 5 of relay STR and front contact t of relay SFP which causes relay SBP to pick up and open at itsl back contact I5 the energizing circuit for the transmitter relay SCTP, thereby preventing any subsequent energization of this transmitter relay SCTP regardless of the closure of the coding con-` tacts until the repeater relay SFP and in turn the repeater relay SBP have released. In other words, after the rst energization of the track relay STR improperly by a code pulse applied to the track section in thevrear, coding is cutoff for a time corresponding with the time that the repeater relay SBP is picked up as indicated i Fig. 3 by the arrows t.

Generally speaking, the effect` of this artificial mutilation of the code is to'prevent energization of the home relay SI-I and clearing of the signal 3. Considering thisoperation more in detail, the release times of the repeater relays SFP and SBP are preferably selected as indicated diagrammatically in Fig. 3 so that the circuit for the transmitter relay SCTP is not rel-closed after this relay 3CTP has once picked up and dropped, until after the contacts of the code transmitter 'I5CT have opened and before'these coding contacts close for the next on period of the 75 code. Regardless of this particular timing, however, it can be seen that the transmitter relay 3CTP cannot be energized again topick up the track relay STR until the back contact repeater relay SBP has released; and .when this,` happens, the energizing circuit for the home relay 3H is open at the front contact 'I of this repeater relay SBP,

, so that such subsequent energization of the track relay cannot cause energization of the home relay SH. In other words, thereis a positive interlock which causes a mutilation of the code delivered to the rear track section to an extent sufficient to prevent improper energization ofthe relay SH.

With regard to the` timing of the repeaterrelays `preferably employed and indicated in Fig; 3, a certain degree of slow action -is required for normal operation. vThe front'contact repeater relay SFP mustl hold over the 01T period .of the lowest code rate, and the release timeof the back contact repeater relay SBP plus the release time of the home relay 3H must hold over the longest .,on period. Thus, the preferable relay timing indicatedin Fig. 3, acting in effect to drop outevery other pulse of the 75 code, is quite consistent with that required for ordinary operation.

From Athis explanation it can be seen that the signicant feature of this invention is that, once a home relay such as 3H has been deenergized by'a train, this relay cannot be energized solely by code pulses delivered to the track section in `the rear and rendered effective to operate the track relay on account of a failure of the insulated joints. This assures that a breakdown of the insulated joints at a signal will not allow the signal to give a false proceed indication behind a train in the same block whose wheel shunt is not effective, or at the entrance to a block next in the rear of an occupied block in the event of a failure of the coding equipment to provide a caution code for the signal in question.

One operating chracteristic of the invention is that the energization of a track relay by code pulses delivered to a track section in the rear because of broken-down joints, or the like, acts lto chop or mutilate this code vto provide time intervals between the successive improper energizations of the track relay longer than the interval between the successive energizations of the track relay required to energize the corresponding home relay H, so that unless an authorized code pulse in the forward section intervenes to pick up the track relay during the blank interval of the mutilated code, the home relay H remains deenergized and the associated signal is held at stop. Stated another Way, the energization of a signal control relay H requires at least two successive energizations of the corresponding track relay TR, with an intermediate deenergized period of a limi-ted delay less than the release time of its repeater relays FP and BP; and when the track relay is improperly energized by the code pulses in the rear ytrack section on -account of failure of the insulated joints or the like and not by authorized code pulses, the automatic chopping or mutilation of the code delivered to the rear section provides much longer deenergized periods of the track relay than are required to energize the signal control relay H. Consequently, regardless of the polarity of the code pulses applied to one track section and the response of the track relay of an adjacent track section to such code pulses due to faulty insulated joints, a false indication of the associated signal cannot be displayed by such code pulses alone. Under normal operating conditions with the insulated joints intact, when the track relay STR, for example, is successively energized by legitimate code pulses, the second code pulse energizes -this track relay before its repeater relay SBP drops and opens the pick-up circuit for the home relay 3H, so that this relay 3H receives successive energy pulses and closes its -f'ront contact I4 to apply code pulses at the 180 rate'to the `track'section in the rear without any mutilation.

Considering now the effect' of an insulated joint failure at signal 3 upon the next signal 2 in the rear, .the presence of a train in the track section T3 with the insulated joints broken down acts to reduce the inter-rail potential supplied by the track battery I2 for the rear track section T2 and thus prevent operation of the Ytrack relay 2TH.; and the resistance of the circuit path around or through the insulated Ajoints and other variable factors determine whether the trackrelay 2TH, will start to operate vbefore Or at'the same time as the track relay v3TH, when vthe Atrain advances.4 If, as assumed for the diagram of Eig. 2B, -the breakdown of the insulated joints atfsignal 3 is so complete that the track relay STR adjacent the track battery will start to operate at least as soon as the track relay 2TR fed from this same battery over the linear resistance of the track rails of the track section T2, then the energization of the track relay 2TR by every other code pulse of the chopped code is just as ineiective to energize the relay 2H as in the case of relay 3H, with the result that the signal 2 likewise remains at stop.

In the case of the second track section TI in the rear, however, its home relay IH is energized by the regular caution code pulses, as indicated in the diagram of Fig. 2A, before the train in track section T3 has advanced to the point where the chopping or mutilation of the code begins; and even though the track relay I TR thereafter may .start to pick up for every other code pulse of the code, due to the action of the repeater ,relay 2BP and failure of relay 2H to pick up, the release time of the home relay IH is long enough to hold over the intervals of such spasmodic energization of the track relay ITR, as diagrammatically indicated in Fig. 3. In this connection, the front contact 'I of the repeater relay IBP is shunted by the front contact 8 of the relay IH, so that energy is applied to the relay IH each time the track relay ITR is energized, even though the repeater relay IBP has dropped in the interval, provided of course that the successive energizations of the track relay ITR occur Within the release time of the relay IH and While its front contact 8 is closed. In other words, while a signal control relay such as 3H in the example assumed cannot be picked up by a mutilated code, once a signal control relay has been energized, as in the .case of the relay IH, it will be held up by the mutilated code by a stick circuit through its from; contact 8 and front contact Il of repeater relay IBPP.

If the track relay ITR should be maintained energized by foreign current or due to other conditions, the release of the repeated relay IBBP and opening of its front contact II will open the stick circuit for relay IH and drop this relay.

It ymay be explained here that, without the stick circuit for the home relay such as just explained in .connection with the relay IH, there would be a tendency for the mutilation of code to Abe repeated or vpropagated through v,the several track sections or blocks in the rear and cause anumber of signals to tumble down and lindicate stop, because the suppression of code Apulses until the repeater relays FP and BP for one signal location have released is likely to prevent energizationof the relay H for the next signal location ldue to the prior or simultaneous release of its ,repeater relays. With the rprovision of kthe stick circuit for home relays H, however, it is possible to maintain any relay H energized, once it has ,been energized, by `'making its release Atime longer than the longest blank or deenergized period of Ya mutilated code.

For the same lreasons that the vrelay IH .when once energized .may be maintained energized in the presence-of a chopped code as just explained, it mayhappen inthe example of vbroken-.down insulated joints under vconsideration that the relay 2H will also be energizedto cause the signal 2 to indicate caution, rather .than stop as previously assumed and shown in diagram of Fig. 2D. This ywilli/occur if the nature ofthe insulatedjoint failure .and track circuit conditions permittlie trackirelay 2,TR .to respond to thecode pulses inthe track section Tzgasthetrain advances beyond the broken-down insulated J'oints, before the track relay 3TR can pick up and start mutilation of the code. Under such conditions, the relay 2H will be energized by normally spaced code pulses, and once energized will remain energized in spite of the subsequent mutilation of these code pulses. With the relay 2H energized', the code in the track section TI is no longer a mutilated code as shown in the diagram of Fig. 2B, but a regular 180 code. In short, if the-home relay 2H gets a chance to pick up before the mutilation of the code occurs, then the signals 2 and l .will indicate caution and clear respectively in the rear of the signal 3 held at stop on account of the broken-down vinsulated joints, such indications' of the signals l and 2 being obviously proper under the circumstances.

In the examplesvof the operation previously explained, it has been assumed that for some reason there are no legitimate codel pulses in the forward track section T3 to operate the track relay 3TR while it is being energized improperly over the broken-down insulated joints by code pulses in the rear track section T2. In other Words, it has been assumed that the operation of the track relay 3TR is dependent solely upon the code pulses improperly applied thereto from the adjacent track section T2 in the rear. vUnder ordinaryconditions, however, when the track 'sectionT3 becomes unoccupied, legitimate code pulses are applied thereto at a rate dependent upon the location of a train in advance, and a-somewhat diiferent operation results.

To illustrate the operation of the system under these conditions, assume that the train as shown in diagram of Figs. 2A and 2B leaves the track section T3, and legitimate code pulses at the 75 code rate are transmitted over the track rails of this track section to operate the relay 3TR in the regular way. Under these conditions, the track relay 3TR is in effect subjected to intermittent energization by currents from two diierentv bat' teries applied at the same '75 code rate by two different code transmitters. While the code delivered by the transmitter relayCTP energized by one of these code transmitters may be chopped as above explained to prevent energization of the track relay 3TR at the frequent intervals required to energize the home relay 3H, it canbe seen that the legitimate code pulses transmitted over the track rails of the track section T3 from the other code transmitter will be normally spaced, with the result that successive cnergizations of the track relay 3TR are bound to occur with its back contact repeater relay 3BP energized, so that the home relay' 3H becomes en#A ergized and causes signal 3 to indicate caution.

Such caution indication of this signal howeve'ixf is due to legitimate code pulses; and since-thesecode pulses cannot exist unless this track section' is not occupied, such caution indication is entirely safe land proper. L

As soon as the signal control relayHis thus energized, another operating condition liscreated-,iy because the transmitter relay T? is then'connected to the 180 code-transmitter, scthatthe' track relay 3TR and alsolto a certain extent;` the i track relay 2TH. is then subjected to the combined effect of code pulses at the 75 and the 180 code rates, as indicatedin diagram of Fig. 2C. Generally speaking, code rates of-75 and 180` com*Y recurrently energized at intervals short4 enough to pick up and hold up a corresponding home relay H. l Consequently, under these conditions, after'ithe'relay 13H picks up and 'its associated track relay3'1'l`1. becomes subject to thelcombined leiiects of and 180 codes, this track relay is repeatedly operated at intervals frequently enough to hold up the relay 3H. f l 1 Theindication displayed bythe next signal 2 in the rear under the conditions under'considerationA is dependent 'ona number of variable fac'' tors, such as the resistance of the circuit path around or through the insulated joints at'the sig'- nal 3, thelength ofthe track sections, ballast resistance, and the like.' Ifthe' code pulses atthe 'l'coderate'from the trackbattery for the forY Ward track sectionvTS 'are eiective to' operatethe' track relay 2TR, 'then this track 'relay is subject to energization' of theregular intervals corre` sponding with the code pattern resulting' from a combination of 75 and 180 codes, and without a succession of `pulses at a definite rate necessary to energize the distantrelay 2D, Withvthe result -that the signa1^2=also indicates caution, as shown in the diagram'ffof Fig'. 2C'. On the other hand, if Vthe current supplied to'the trackrelay ZTR from the remote track `'battery off track section T3 over the track rails -of both track sections is not strong enough-'topick up or hold up the.v track relay' 2TR, then thistrack relay -may 're-f spond to the 180 code pulses in thetrack section T2 to cause signal 2 to indicate clean- .-Such clear indication of the signal 2, however, is safe' combined eiect of .ftwo codes at the same 180 rate*- fromtwo different code transmitters, as ldiagram-- maticallyvindicated inv the-diagram 'ofiFigfZDf- On account of variations infmanufacture and adjustment, the exact code rates from two different code transmitters are usually slightly diierent'y` and generally speaking,` these transmitters hunt,` (d into and out of Yphasef-at intervalsto give periodsl of uneven-coding. and prolongedl energization of" the track relay `3Tl\;lsulicient'to release distanty relay 3D. For-'examplaifone code` transmitter? operatesiat the regularr'ateof- 180 times 'a'minute,=.` whileA the other operatesrslower at =179 timesa" minute, it can be appreciated that theefaster code-V transmitter will-gain over the other one'complete'fl cycle or code'element once every minute, orthe equivalent of oneon'interval every half minute. 55 Consequen`tly,'if"fthese different codetransrriitters at agiven'instant are `acting to energize thetrack': relay S'I'Ratthe Sametime at the 180 rate, and. the distantfrelay 3D becomes energized," therei. after-the faster oscillatory acts to start 'each'sucefg cessiveenergization a little `earlier' tomake they energized periods of thetrack relay `3'I'Rprogres.` sively longer, kand the off intervals shorter; so that afterabout a halfa minute the .on periodi.' provided by the one 'code transmitter occurs 'dur-L ing'the off"period of the othe'nand givessuch prolonged Aperiods of energization and? short periods of deenergization that'the home relay is likely to be released. 'The same will betrue for the home relay-2H forthe signal 2 in the rear', if thecurrent fromv the ftraek battery for track-'"1 section T3 is vsuilicient to operate thetrack relay 2TR asassumed. *Inl short,` as v diagrammatically* indicated-inthe' *diagram* of Fig. 2D, under ther conditions assumed; itV is'` likelyf that thesignals* 21 and 3 Will intermittentlyVV indicate clear' and -1 stop. When the home relay 3H releases, the code in track section T2 is changed to the "lcode rate, which will combine with the 180 code rate in track section T3 to restore the home relays 2H and 3H rather quickly; and it is likely that the distant relay ID will hold over the change in code rate in track` section TI dueto the intermittent operation of the home relay 2H and will give a steady green indication. If, however, the code pulses from the track battery for track section T3 are not strong enough to pick up or hold up the track relay 2TH., then it will respond in the normal way to the code pulsesat the 75 and 180 code rates as applied by the intermittent operation of the home relay 3H; and the signal 2 will intermittently indicate clear and caution, while the signal I gives a steady clear indication.

This intermittent change in signal indications or pumping action of signals in the case of an insulated joint failure has the advantage of indicating the abnormal'condition tothe engineers of subsequent trains, and enables the insulated joint failure to be reported .and repaired promptly, without waiting until the abnormal condition is detected by test o r inspection. In this connection, it should be understood that the clear indications temporarily displayed under these conditions in the absence of trains are safe and proper.

In connection with this manifestation of broken-down insulated joints characteristic of the invention, it should perhaps be explained that in the ordinary block signaling system when a train approaches a signal at which the insulated joints are broken down, the shunting action of its wheels and axles acts While approaching these joints to produce a shunting effect upon the track relay governing this signal and tends to cause it t'o indicate stop before the train reaches it.I In other words, in the ordinary block signal system, a failure of the insulated joints is frequently manifested by an abnormal stop indication in theface of an approaching train. The fact'that the signal goes to stop in the front of a train when the insulated joints are broken down does not, how:- ever, afford adequate protection for train movement, because Without the protective features of section. The expedient previously mentioned of staggering the polarities on opposite sides of the insulated joints serve to' accomplish a Vsimilar purpose when ther 'code pulses are of Aa xed polarity and the track relay is responsive only to an opposite polarity; but the protective features of this invention enable the polarity of the code pulses applied to the track section. either as driven or off code pulses to be changed under different conditions to provide somedesired distinctive controls. without risk of a vfalse signal indication if the insulated 'joints should break down. For example, it may be desired to provide driven code pulsesof different polarity at differ-l ent times in a given track section such as T2 for special control purposes, using polar track relays for this track section distinctively responsive to these different polarities; and under these conditions, without the protective features of this invention', it can be seen that if there is a breakdown of the insulated joints at signal 3, the track relay STR will necessarily be operated by one or the other of these polarities, and similarly if the insulated joints at signal 2 should break down, code pulses in the track section TI of a fixed polarity would necessarily cause operation of one or the other of the track relays for track section T2 responsive to different polarities. While the protective features of the invention are of particular use in such an organization employing code pulses of different polarities, no attempt has been made to illustrate any one of the various forms which such an organization may take, since it is obvious how the invention may be applied to such organizations.

The characteristic features and operating prin'- ciples of the invention may be employed in different ways in connection with various types of coded track circuit systems; and I desire to have it understood that various modifications and additions may be made in the specific embodiment of the invention shown and described without departing from the invention.

What I claim is:

l, In a coded track circuit signaling system for railroad tracks divided into adjoining track sections electrically separated by insulated joints, a signal at the entrance to the forward track section for governing train movement into that track section, a code following track relay connected across th'e track rails at the entrance end of the forward track section, code transmitting means for applying code pulses to the track rails at the exit end of the rear track section, decoding means for governing the indications of said signal and including relay means energized to permit said signal to give an indication more favorable than stop only if said track relay is successively energized at intervals less than a predetermined time period, and means responsive to the energization of said track relay for ren-` dering said code transmitting means ineiective for a time longer than said predetermined time period, whereby in the event of a breakdown of said insulated joints said signal cannot be cleared by the code pulses alone applied to the rear track section by said code transmitting means.

2. In a coded track circuit signaling system for adjoining track sections electrically separated by insulated joints, a code following track relay connected across the track rails of the forward track section on one side of said insulated joints, decoding means responsive to the intermittent operation of said track relay and including a slow-release signal control relay energized only if said track relay is successively energized at intervals less than a predetermined time, code transmitting means for applying code pulses across the track rails of the rear track section on the other side of said insulated joints at a Icode rate dependent upon the energized or deenergized condition of said signal control relay, and means poverned by said track relay for preventing energization of the track rails of said rear track section independently of the operation of said code transmitting means for a time longer than said predetermined time, whereby in the event of failure of said insulated joints said signal control relay cannot be energized by the coding in the rear track section alone.

3. In a coded track circuit signaling system for railroads, the combination withv two adjoining track sections electrically separatedby insulated joints, a code following track relay for the forward track section, decoding means including a slow-acting signal control relay initially energized by successive energizations of said track relay only if said energizations recur within a predetermined time, code transmitting means normally acting to apply code pulses t the rear track section at a certain code rate while said signal control relay is deenergized, and means effective only while said signal control relay is deenergized and responsive to the energization of said track relay for mutilating the code pulses that would otherwise be applied to the rear track vsection and thereby provide blank intervals longer than said predetermined time, whereby said signal control relay cannot be initially energized in the event of failure of ther insulated joints when said track relay is operated by the energization of the rear track section alone.

4. In Aa coded track circuit automatic block signalingsystem for railroads having track sections electrically separated by insulated joints, a signal at the entrance to each track section governing train movement in one direction, a code following track relay connected across the track rails at the entrance end of each track section, decoding means for each signal including a slowrelease signal control relay responsive only to successive energizations of the corresponding track relay occurring within a limited time, code transmitting means for supplying code pulses to each track section at a rate determined by the energized or deenergized condition of the signal control relay for the next block in advance, and means for rendering the code transmitting means for any track section ineffective for a time longer than said limited time while the signal control relay for the next block in advance is deenergized, and thereby prevent energization of that signal control relay if the associated insulated joints break down and the corresponding track relay is operated solely by energization of the track rails of the adjoining track section in the rear.

5. In a coded track circuit system for adjoining track sections electrically separated by insulated joints, a code following track relay for the forward track section, decoding means responsive to the coding operation of said track relay and including a slow-release signal control relay, said signal control relay being initially en l..

ergized only by successive energizations of said track relay recurring in less than a predetermined time and being maintained energized by successive energizations of said track relay at longer intervals, code transmitting means normally acting while said signal control relay and said track relay are both deenergized to apply regularly spaced code pulses to the rear track section, and means effective while said signal control relay is deenergized and responsive to the energization of said track relay for mutilating the code pulses supplied to the rear track section to provide blank periods of deenergization longer than said predetermined time required for the initial energization of said signal control relay but less than said longer time intervals required to maintain said signal control relay energized.

6. In a coded track circuit signaling system, the combination with adjoining track sections separated by insulated joints, a code following track relay for the forward track section, a code transmitting relay acting whenr energized to'apply a potential across the track rails of the rear track section on the other side of said insulated joints, a code transmitter operating coding contacts at a predetermined code rate, a circuit for connecting said coding contacts with said transmitter relay, means responsive to an initial ene'rgization and deenergization of said track relay for opening said circuit and maintaining it open for a predetermined time after the deenergiza-4 tion of said track relay, and a-signal lcontrol relay governed by said means and initially energized only when said track relay is successivelyenergized at intervals less than said predeter release back contact repeater relay, circuit means including a back contact of said track relay and'v a front contact of said front contact repeater relay for energizing said slow release back contact repeater relay when said track relay is deenergized if said front contact repeater relay is then energized, and code transmitting means for applying code pulses to the rear track section having an operating circuit including a back con- 4 tact of said back contact repeater relay.

8. In a coded track circuit signaling system for railroads having track sections electrically separated by insulated joints, a code following track relay for each track section, a slow release front contact repeater relay associated with each track relay, circuit means for each front contact repeater relay including a front contact of its associated track relay for energizing such slow releasef front contact repeater relay when said trackj relay is picked up, a slow release back contact repeater relay associated with each track relay, energizing circuit means for each back contact repeater relay responsive to the energization of its associated track relay and including afront. l: contact of the associated front contact repeaterv relay, a signal control relay for each track sec-- tion, circuit means for each signal control relay for initially energizing that relay in response tothe energization of the associated track relay only if the corresponding back contact repeater relay is then energized, said signal control relay when once energized receiving energizing current in response to the energization of said track relay independently of the condition of the corresponding back contact repeater relay, and code transmitting means for applying code pulses to each track circuit and having an operating circuit including in series back contacts of the signal control relay and the back contact repeater relay for the next block in advance.

9. In a coded track circuit signaling system for railroads, the combination with adjoining track sections electrically separated by insulated joints, a code following track relay for the forward track section, a signal control relay initially energized only if said track relay is successively energized at intervals less than a predetermined time, code transmitting means normally acting to apply regularly spaced code pulses to the rear track section while said signal control relay is deenergized, and means responsive to the initial energization of said trackT relay for governing said code transmitting means to eliminate a code pulse and thereby produce a blank period of deenergization of the track rails of the rear track section longer than said predetermined time, whereby in the event of a breakdown of said insulated joints said signal control relay is not energized when the track relay is operated solely by the energization of the track rails of the rear track section.

10. In a coded track circuit signaling system for adjoining track sections electrically separated by insulated joints, a code following track relay for the forward track section,y a slow-release repeater relay governed by said track relay, decoding means including a slow-acting signal control relay energized only if saidV track relay is successively energized with an intervening deenergized periodof limited duration, code transmitting means normally acting to apply regularly spaced code pulses to the rear track section, and means governed by said repeater relay and effective while said signal control relay is deenergized for preventing energization of the track rails of said rear track section by said code transmitting means for periods longer than those required for the energization of said signal control relay.

l1. In a coded track circuit signaling system for railroads, the combination with two adjoining track sections electrically separated by insulated joints, a transmitter relay acting when energized to apply code pulses to the rear track section, an energizing `circuit for said transmitter relay including intermittently operated coding contacts, a code following track relay for the forward track section responsive to code pulses applied to the rear track section in the event of a breakdown of said insulated joints, signal control means energized by successive energizations of said track relay only if such energizations occur within a limited time interval, and a slow-release repeater relay governed by said track relay and having a back contact included insaid energizing circuit for preventing energization of said transmitting relay for a time longer than said limited time interval.

12. In a coded track circuit automatic block signaling system for railroads, the combination with adjoining track sections, a signal at the en- `trance to the forward track section, a code following track relay fcr the forward track section, a transmitter relay having an energizing circuit including coding contacts for applying code pulses to the rear track section, a slow-release signal control relay having an energizing circuit governed by said track relay, said signal control relay when deenergized preventing said signal from giving an indication more favorable than stop, and means responsive to the operation of said track relay and-elfective only while said signal control relay is deenergized for alternately closing the energizing circuit for said transmitter relay and the energizing circuit for said signal control relay, whereby operation of said track relay solely by coding of the rear track section in the event of a breakdown of said insulated joints is not effective to energize said signal control relay and cause the signal to give a false indication.

13. In a signaling system of the character described, the combination with adjoining track sections electrically separated by insulated joints, code transmitting means for applying regularly spaced code pulses to the rear track section, a code following track relay for the forward track section, a signal control relay energized only if said track relay is successively energized within a limited time, and means effective until said signal control relay is energized upon the initial reception of code pulses by said code following track relay for governing said code transmitting means to provide blank periods between the code pulses longer than said limited time.

i4. In a coded track circuit system, the combination with a plurality of track sections electrically separated from each other by insulated joints, a code following track relay anda code transmitting relay for each track section, an operating circuit for each transmitter relay including intermittently operating coding contacts for energizing said relay to apply code pulses to the corresponding track section, a signal control relay for each track section having a pick-up circuit energized in response to the energization of the corresponding track relay, a slow-release repeater relay governed by each track relay and acting to close alternately the operating circuit for the code transmitting relay for the next track section in the rear and the pick-up circuit for the associated signal control relay, and a stick circuit for energizing each signal control relay in response to the energization of the corresponding track relay independently of the associated repeater relay.

' 15. In a coded track circuit system, the combination with adjoining track sections electrically separated by insulated joints, a transmitting relay acting when energized to apply code pulses to the rear track section, a code following track relay for the forward track section, an energizing circuit for said transmitter relay including intermittently operated coding contacts, and means governed by said track relay for temporarily opening said energizing circuit independently of said coding contacts to eliminate alternate code pulses that would otherwise be applied to said rear track section.

WADE H. REICI-IARD. 

